It is widely known that gasoline and water do not mix. This means that water, when added to gasoline, forms a separate liquid phase which contains virtually all the water and a very small amount of gasoline, and is generally termed the “water phase”. The other phase, the “gasoline phase” contains a very small amount of water. The water phase has physical properties that are totally different from the gasoline phase. The density of the water phase at ambient conditions is typically 1000 kg/m3, whereas the density of the gasoline phase is typically 700 kg/m3. The interfacial tension between the water phase and the gasoline phase is typically 0.055 N/m. This means that droplets of the water phase in the gasoline phase have a strong tendency to coalesce. Furthermore, the density difference leads to a rapid disengagement of the two liquid phase into a lower water layer and an upper gasoline layer. The presence of a separate water layer is generally known to be harmful to systems for fuel storage and distribution, car fuel tanks, fuel injection systems and related systems.
Gasoline and anhydrous ethanol are miscible in any ratio, i.e. they can be mixed without occurrence of a separate liquid phase. When a certain amount of water is present, however, a separate liquid layer will occur. The maximum amount of water that does not cause a separate liquid layer to appear shall be known here as the “water tolerance”. The occurrence of a separate liquid phase in gasohol is perceived as harmful even though the phase behavior of gasoline—ethanol—water mixtures is totally different from gasoline—water mixtures. There are several inventions on the subject of preventing the occurrence of a separate liquid phase, also known as “stabilizing”. U.S. Pat. No. 4,154,580 describes a method for producing stabilized gasoline—alcohol fuels by chemically hydrating the olefinic gasoline constituents to alcohols, which increases the water tolerance. U.S. Pat. Nos. 4,207,076 and 4,207,077 describe a method to increase the water tolerance of gasohol fuels by adding ethyl-t-butyl ether or methyl-t-butyl ether, respectively. U.S. Pat. No. 4,490,153 describes a manufacturing procedure for gasohol fuels using liquid-liquid extraction operated at −10° F. (−23.3° C.). Gasohol produced at these low temperatures are stable at all temperatures above −10° C.
All methods, such as the ones described in the aforementioned patents, employ major operating facilities, such as reactors, distillation columns, extraction columns and vessels and heat exchangers. Also they use substantial amounts of energy such as steam and electricity and skilled personnel is required to start-up, control, maintain and shut-down such processing facilities. Furthermore said operating facilities produce waste materials such as a wastewater that contains ethanol and gasoline, and that must be sent to wastewater treatment facilities or waste incineration facilities, before disposal into the environment. The necessity of said facilities restricts the manufacture of gasohol to areas where such facilities are present, for example a refinery. In many regions, however, it is preferred to manufacture gasohol by simple blending at a fuel distribution terminal or other sites where said processing facilities are not present.
The perceived harmfulness of a separate liquid phase drives gasohol manufacturing companies to the use anhydrous ethanol.